The Russian government has pinned the "foreign agent" label on a long-haul truckers organization that has been holding protests against a road tax since 2015.

The Justice Ministry said on December 1 that a surprise inspection of the United Truckers of Russia's documents revealed evidence that it "carries out the functions of a foreign agent."

The ministry's brief statement gave no further explanation and did not name any country or foreign organization that was allegedly funding the group.

The NGO was established after truckers across Russia began nationwide protests against the Platon road-tax system in late 2015.

United Truckers head Andrei Bazhutin said last month that the group plans to start a new series of protests in mid-December, ahead of the registration of candidates for Russia's March 18 presidential election.

A 2012 law requires any NGO that receives funding from abroad and is deemed to be engaged in political activity to formally register as a "foreign agent." A 2014 amendment enables the Justice Ministry to place groups on the list itself.

Russian and international human rights organizations have said the law was introduced to silence independent voices.

They describe it as part of a clampdown on dissent under President Vladimir Putin, who is expected to secure a new six-year term in the election.